1. Field of the Invention
The present invention relates, generally, to light modules for motor vehicle headlamps and, more specifically, to a method for calculating the surface area of optical lenses and projection lenses manufactured according to the method for use in a light module in a motor vehicle headlamp.
2. Description of the Related Art
Projection lenses known in the art used with light modules in motor vehicle headlamps are typically designed to project at least a portion of light emitted from a light source in the light module onto a road surface in front of the motor vehicle so as to generate a low beam light distribution.
In the field of motor vehicle lighting devices, in particular in the field of motor vehicle headlamps, one can, in principle, differentiate between two different types of light modules. With so-called reflection modules, the desired light distribution on the road surface in front of the motor vehicle is generated with a reflector, which reflects the light emitted by the light source onto the road surface in order to generate the desired low beam light distribution. With projection modules, an additional projection lens is disposed in the beam path and projects the light bundled by the reflector or other type of primary lens, for generating the desired low beam light distribution onto the road surface in front of the motor vehicle. In order to generate the low beam light distribution, typically an aperture assembly is disposed between the primary lens and the projection lens, wherein an upper edge of the aperture assembly is designed to generate a light/dark border in the low beam light distribution from the projection lens onto the road surface in front of the motor vehicle.
Reflection modules have different sized light source images in the resulting light distribution, due to different spacings and perspectives of light sources and reflector ranges. These differently sized light source images can be used well in the configuration of a reflection module of this type for making use of the light source images in order to illuminate different regions in the resulting light distribution. As such, the use, for example, of small light source images for creating the light/dark border in the low beam light distribution and to obtain the largest possible range for the light distribution is known in the art, in that the small light source images are reflected to a position in the light distribution that is as close as possible to the bottom of the light/dark border. Large light source images, conversely, are frequently used to illuminate the foreground or close-range in front of the vehicle, as well for illuminating the lateral regions in the resulting light distribution. In particular, the desire to direct light into the distance, directly beneath the light/dark border, so as to obtain a greatest possible range for the resulting light distribution, is only possible with the smallest possible light source images.
With projection modules, reflectors or other types of primary lenses are used for bundling the light emitted from a light source. As such, the use of lens systems or so-called adapter lenses, for example, is known in the art. Adapter lenses are normally manufactured from transparent glass or plastic material, in which the light emitted from the light source is coupled. The coupled light is, at least in part, subjected to a total internal reflection at the outer border surfaces, and then exits the adapter lens. The portion of the coupled light not subjected to a total internal reflection preferably exits the adapter lens directly. The bundling of the light occurs thereby through refraction at the light entry and/or light exit surface, and through the total internal reflection at the border surfaces of the adapter lens.
Further, secondary lenses are used with projection modules, in order to image the bundled light onto the road surface, and to generate the desired low beam light distribution. The secondary lenses can be designed as reflectors or as projection lenses. The projection lenses can image the light distribution, generated with the bundled light in an intermediate plane, into the distance, or can be designed as a so-called direct imaging system.
With direct imaging projection modules, a light source, which may include one or more light emitting diodes (LEDs), for example, is imaged onto the road surface via the projection lens, without the need for further optically active surfaces for bundling or deflecting the light beams. Direct imaging projection modules of this type generate light distributions with a suitable shape of the projection lens, which exhibits a defined expansion in both the horizontal and vertical direction.
In addition, projection lenses known in the art may be designed so as to generate a low beam light distribution having a substantially horizontal light/dark border without an additional aperture assembly disposed in the beam path. In this way, the light/dark border can fulfill the ECE, SAE, or any other government-mandated requirements.
The projection lenses known in the art for use in light modules for a motor vehicle headlamp are shaped such that one side of the lens is either planar, convex, or concave. In this case, the divergence of the light beams exiting a known projection lens is nearly uniform over the entire light exit surface of the projection lens. The images of the light source with a projection lens of this type all have a similar size on a measurement screen disposed at a spacing to the light module, or to the motor vehicle headlamp, respectively. As a result, the projection modules differ significantly from the reflection modules.
As a result, with the nearly same sized light source images generated by a projection module, it is not possible, in generating the resulting light distribution from a projection module of this type, to deflect differently sized light source images in different regions of the resulting light distribution. In particular, there are no particularly small images that can be used to generate a large range for the light distribution, and there are no particularly large light source images that can be used to illuminate the foreground or lateral illumination areas in the region of the light distribution. In order for the resulting light distribution of the projection module to therefore fulfill the demanded customer requirements, it is known from the prior art to deflect the basically same sized light source images into the desired regions of the light distribution, without affecting their sizes. In particular with the known projection modules, a satisfactory foreground illumination is only possible by lowering the relatively small light source images. This means that light source images from one region need to be pushed downward, to directly beneath the light/dark border in the foreground of the light distribution. This results in a weakening of the range and the gradient at the light/dark border.
It would be theoretically possible to modify the imaging scale via the spacing between the light source and the projection lens. In order to obtain small light source images, the spacing would then need to be increased. This, however, would necessitate enlarging the projection lens transverse to the beam direction, in order to accommodate the same spatial angle with respect to the light source. Alternatively, with the same dimensions transverse to the angle of radiation, less light passes through the projection lens, weakening the efficiency of the projection module.
Thus, there remains a need in the art for a method for calculating the surfaces of optical lenses, a projection lens, a projection module, and/or a motor vehicle headlamp in this respect, such that imaging systems with different imaging scales can be generated, wherein different sized light source images are available which can then be deflected in a targeted manner into the desired regions of the resulting light distribution. In particular, it is desirable to have smaller light source images available for illuminating the region of the light distribution directly beneath the light/dark border, and larger light source images available for illuminating a region of the light distribution in the foreground and/or the lateral regions of the light distribution, with a direct imaging projection module.